Visited the Steward tunnel last September.  Beware of parking, I got a $175.00 parking ticket but it was still worth it.  When you are in the middle of the tunnel, its curved so much you cannot see either exit.  Very popular spot located along a state hiking trail.

N 42° 48.671 W 089° 33.995
16T E 290157 N 4743042

Stewart Tunnel, also known as the Belleville Tunnel was located along Illinois Central line. Located 4 miles southwest of Belleville,WI this former rail line is now the Badger State Trail.

The tunnel was built in a curve so you can’t see the other side when approaching. The tunnel is named for James Stewart of Lancashire, Pennsylvania. Stewart, who was contracted to build the rail line was killed when he was thrown from a buggy while driving over the proposed route. Construction of the tunnel was completed on January 26, 1888.
Photos taken in September 2011
Trail leading to the tunnel

Entrance of the tunnel:

Tunnel interior:

The other side